Custom, Performance Carb Intake Manifolds ( 2bbl / 4bbl )

-Just for Reference-
For A 4BBL manifold you would want to increase the runner diameter. The stock diameter is too small.

I was reading up some and found that I could increase the CFM the engine pulls by 52 if I divide the cylinders into pairs.

Below 3,600 rpm the divided plenum manifold makes more HP and Torque
Above 3,600 rpm the open plenum makes more HP and Torque

A20 @ 100% VE is good for 224 CFM @ 6,500 RPM
22R @ 100% VE is good for 270 CFM @ 6,500 RPM

The vacuum secondary 390 CFM 4bbl conversion for the 22R uses a DUAL PORT MANIFOLD which is sort of what our stock manifold tried to do. I'm guessing that having the primaries and secondaries seperated up untill the runner meets the port helps a 270 CFM motor run a 551.5 CFM carb. It probably has a simmilar effect as a dual plane but without sacrificing the top end by having access to all 4 barrels.

The A20 would peak at 276 @ 6,500 with a DIVIDED PLENUM 4bbl manifold... but we just barely inch over the 390 CFM 4BBL's rating of 275.75. Because of this it's probably better to stick with the 390 since you'll have an easier time jetting it and it will be more responsive. If you plan to rev to 7,500 then you'll get about 310.25 CFM with the manifold, but you're still closer to the 390 4bbl than you are to the 500 4bbl.

Lets see if I'm doing this right

2bbl and 4bbl are rated differently for CFM

2bbl CFM = 4bbl CFM x 1.414
4bbl CFM = 2bbl CFM / 1.414

(I'm rounding to the nerest 0.05)
So the divided manifold would make the 4bbl into two 2bbl's

390 CFM 4bbl converted to 2bbl is 551.5 CFM but since it's split into two I divide by 2 right... so then I get two 275.75 CFM carbs which is just like having two 2bbl Keihins each feeding 2 cylinders.

500 CFM 4bbl converted to 2bbl is 707 CFM but since it's split into two I divide by 2 right... so then I get two 353.5 CFM carbs... which is just like having two 38 Webbers each feeding 2 cylinders.


https://www.3geez.com/forum/attachmen...tid=3485&stc=1
* This shows the vacuum port for the rear of the manifold in the center and also the brake booster port to the left of it. The 4bbl adapter is placed on top of the manifold.

https://www.3geez.com/forum/attachmen...tid=3486&stc=1
* This pic shows me messing up and installing the adapter in the wrong orientation. The center divider to divide the plenum is insterted but not really permanent.

https://www.3geez.com/forum/attachmen...achmentid=3487
* This pic shows the correct orientation.

https://www.3geez.com/forum/attachmen...achmentid=3882
* This pic shows the bolts securing the manifold... x2
5/16" shaft with 1/2" Head.


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https://www.3geez.com/forum/attachmen...tid=3483&stc=1
* This pic shows the DGV Weber adapter, notice that the center wall has a chunk taken out of it, otherwise the rest of the port was left untouched.
* This mod can be used with JAM ENGINEERING ADAPTER to use 1 WEBER DCOE.

https://www.3geez.com/forum/attachmen...tid=3484&stc=1
* This pic shows the DGV adapter on the manifold ported to accept the 4bbl, notice that the center wall was shaved down, but so was most of the original manifold port as well. It's possible to remove the center wall entirely... and only widen the port enough to match the port on the DGV adapter plates.


POSSIBLE STOCK MANIFOLD MODIFICATIONS

1bbl X 1bbl Manifold ( BIKE CARBS )
https://www.3geez.com/forum/attachmen...achmentid=3879

2bbl X 2bbl Manifold ( 38/38 WEBER CARBS )
https://www.3geez.com/forum/attachmen...achmentid=3880
https://www.3geez.com/forum/attachmen...achmentid=3884
* The pic shows a 32/36... a 38 will be used instead and it will face the other way so that the fuel neck doesn't hit the valve cover... I used that orientation in the pic because I had an elongated throttle shaft.
* This mod can be used with JAM ENGINEERING ADAPTER to use 2 WEBER DCOE's.


4bbl - 2bbl X 2bbl Divided Plenum Manifold ( DOMESTIC 4BBL CARBS )
https://www.3geez.com/forum/attachmen...achmentid=3881
* This mod can be used with JAM ENGINEERING ADAPTER to use 2 WEBER DCOE's.

I hope to get pics from Phydeaux to complete his project.

Quote:

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Originally Posted by PhydeauX

I'm just toying around with an idea that I'm not sure will work yet but I'll throw it out here anyway. I remember a few people talking about making a performance manifold for the Weber DGV I got thinking and started looking into things. Making a new manifold wouldn't really be practical. It would be harder to make, i.e. cost more, then a DCOE manifold. The way I see it if people could afford the DCOE manifold why would they bother with a DGV. Basically what I'm doing is modifying the stock manifold to have a larger plenum and accept a Weber carb without an adapter. I making this with the DGS in mind but a DGV will be able to work on it with no problems. Basically I'm grinding out the plenum area. Not just the dividing walls but also the whole plenum area, removing the top and all reshaping it for max volume. Then I plan to weld a new top on the plenum ready to accept the DGV series carb. This manifold should give the car better breathing up top and be good on a stock or mild cam engine. I have no idea on pricing yet. Most likely it will be less then $200. I just started making the prototype and I'll have a better feel once that’s done. I'll probably also put a $50 core on it so those who buy one will send me their old manifold. Manifolds are such a pain in the ass to get off at the junkyard.

A few updates. I might consider making the manifold to fit a DCNF if the interest so arises. The DCNF is a 2 barrel down draft carb usually found on Italian V configured engines, Lambo, Ferrari, etc. The common bore sizes on e-bay are 40 or 42mm, though they came in 36, 40, 42, and 44mm versions. Used they don’t tend to cost any more then a DGV. The carbs are performance carbs and are fully tunable. The available choke sizes range from 23-38mm. The DGV uses a 26 and 27 mm choke, not changeable, and the DGS uses 2 27mm chokes, also not changeable. This could prove to be a rather potent setup.

It should clear the hood using a short stack. It’s no taller then a DGV, which is why I'm thinking about it instead of an IDF or IDA series carb. The bores are also closer spaced making it fit the plenum better. The way I am setting this up there will be no adapter plate so the carb will sit closer to the manifold to help with clearance issues as well. The only major concern I have is that the carb will be sitting sideways. The throttle shaft is supposed to sit parallel to the crankshaft on an inline engine; the DCNF will be sitting perpendicular. I've read that this can cause issues with uneven distribution of mixture to the cylinders, but I don't think it will be an issue here with the enlarged plenum. Though the only way to find out is going to be when I finish building it and test it out. I already have a manifold that I'm using as a prototype but thanks anyway.

The throttles sit sideways. When they are only partially open fuel only comes through the side that is tipped down. That puts it closer to the 1-2 half of the manifold then the 3-4 half. That could pose a problem with cylinders 3 and 4 getting a weaker mixture at partial throttle. I'm not sure how much of a problem this will be. As you can see in those pics the plenum is now cavernous compared to what it was before. I think that will cancel out some of the effects. I want to stick with the DCNF because of its tunability and compact size. Ideally I'd like to use an IDA but that’s not feasible. I saw a carb on e-bay labeled 40 DFO. It looks like a cross between a DCNF and a DGS. I can't find any info on it; it doesn't even make it into my Weber book. If its what I think it is then this carb would be perfect. The one on e-bay is in sad shape and way over priced so I'm not going to bother, besides its too rare. I'm going to give it a shot with the DCNF and see what happens. If it doesn’t work out then I'll settle for a 38/38 DGS. There's probably a chance that I'll make some for the DGV anyway just because I think I'll have a better chance of selling them.

My DCNF came today. I must say it fits the manifold like a glove. The outside dimensions are almost the same as a DGV carb. I have just a bit of work left to do before the prototype manifold is complete. Then its testing time.

The manifold still isn’t completed. I drilled one of the holes crooked when I was doing the studs. I've made a plug for it but I haven't got around to actually plugging and redrilling the hole. I'm going to wait until I can either get access to or just finally buy a drill press to finish it.

I'll assume it will give some sort of gain with a DGV. The whole reason I started this was to fit a DCNF carb to the car to offer a cheaper performance alternative that was some where in between a DGV and a DCOE conversion. I toyed around with making some studs for the DGV because theoretically it should give some gains in the upper rpm. I never ran the numbers to see if it was worth it though. It would also eliminate the need for an adapter plate, which can be the source for numerous vacuum leaks. The car would also sit about half and inch lower allowing you to run the taller air filter, which may or may not make a difference. I always ran a taller one, but then a gen2 doesn't have the clearance issues a gen3 does.

I'm not sure if I'm even going to test this setup on my car anyway. I know it will be a step down from what I have now, but I might like a comparison as to how close it comes. I already have a tester lined up to run it on a stock motor when ever I get it done so don't even ask ;-b.

Andy

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i'm not very knowledgable of carbs, but this reminds me of an H22 or B18C intake manifold, with dual runners for each cylinder. (except they have butterfliy valves, and you don't.) many people that want to keep the stock H22 or B18C intake manifold remove the butterflies and do a nice p&p job. some go as far as to remove the wall separating the runners, making one very large runner for each cylinder, rather than having two. this reveals a lot more power than dual runners for those manifolds.

it sounds like a cool project tho. if your math is correct, it looks like it would outflow pretty much any carb on the market for this engine. be sure to portmatch this bad boy to the head! i'd like to see dyno results comparing your carb/manifold and other aftermarket carbs. cool idea.

i say you def put that on the dyno after all this is done. i'd really like to see your design outflow a reputable carb company's design. then post those dyno numbers up! if you can't afford a few runs, ask around the site for some donations. its not something i would do since i don't seem to be very well liked on this site at the moment, but you seem like an upstanding 3geez resident. i'm sure most people wouldn't mind throwing in a few dollars here and there in the name of research and development. i'd throw a few bucks your way.

I found a #7455 450 HOLLEY ECONOMASTER QUADRAJET CARB on e-bay... I'm hoping to get some money soon but it may not be in time for the auction... :(
I'd need a bigger pump too.

It should be about 318 CFM for each side of the manifold with the divided plenum.

STAHLE

http://ftl.realbig.com/pipermail/det...er/018416.html

390 4160
450 CFM
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Has anybody looked into the Holly 2300 2 barrel carb. Its a great carb comes in 350 and 500 cfm versions. There real popular with circle teack racer and drag racers that require a 2 barrel carb. They take all the standard holley parts. Usually about $200 from Summit or a reman for $150 there selling now.
I have had great luck with them on all kinds of v-8 cars that need a new carb.

The Quadrajet is a good 4 barrel carb it has very small primaries then the big sucker back barrels. The backs are vacuum operated. There real popular on Chevy's cars and trucks any junkyard should have a bunch. There harder to tune and there arent many parts for them as far as jets a rods.

wp

I need to find that other spare intake manifold I had laying somewhere.... Mike I think I caught the bug for this ;) What kind of fuel pump would you need for a quadrajet? Or one of those 2 barrel holleys? I was arranging to buy a carter fuel pump for my weber carb but I wont buy it if I wouldnt be able to use it with a bigger carb.

So basically Mike you got one of those 4 barrel carb adapters from a parts store and you just started fitting it and cutting to match the intake right? I'm definately going to need some bigger performance parts since I will be staying carbed :) Keeping the dream alive!

-Mike

Couldn't you buy one of those 2 to 4 barrel adapters? I was thinking about this and I know hoodline would be a problem but that's more reason to have and ram air hood cowl with and big ass air cleaner :)

I have a machine shop at my school at my disposal and will basically do almost everything for free. I could have them make the plates to go from our stock manifold to a 4 barrel adapter. Would this be ok or would that be too restrictive? I know having less adapters is best but sh*t if we had a 500+ cfm 4 barrel I highly doubt we would notice any lost performance and it would be a heck of a lot easier than trying to just fit a 4 barrel adapter to the stock manifold. I'm real serious about this Mike so let get this thread rollin! I would prefer a 4 barrel with electric choke and for a manual trans. I've seen a ton of good deals on ebay they just need to be rebuilt and I've rebuilt many carbs already so thats no biggie. What brand should we stick to or doesnt it matter?

-Mike

My god the possibilities :crying:


http://cgi.ebay.com/ebaymotors/ws/eB...category=33551

That would sure fix the hood clearance problem :) But probably get my a$$ kicked by the muscle car guys in town :(

mikelx... you have machine shop access... can you weld a manifold? for DCOEs...

I've only welded once so I don't think I will be welding any manifolds :) Now if my dad broke down and finally gets a welder again he could definately do it. He's been welding for like 35 years so he's pretty good. And he can do aluminum too. He used to weld aluminum truck tool boxes out in Oregon at Highway Products.

But if you're wanting me to get some flanges made I could probably do that if you give me the exact dimensions you need.

I should have brought this up before but I thought I read somewhere at school if you have too big of a carb for the engine the engine won't perform well. I think it had like the size of the motor and then had what cfm would be ok to use for a carb. The carbs I have been looking at getting are anywhere from 600 cfm to 800 cfm. What carb sizes and brands are you guys looking at getting?



edit: I found my spare intake manifold :) So I'm going to go out and buy a quad carb adapter kit. And start the measuring process. I would like to figure out a way to make some sort of adapter plate to fit onto the stock manifold to fit a quadrajet carb. This way it can give other carbed accord members a better chance at having a big carb. I know it probably wouldn't flow the best but it would still be better than stock and the weber 32/36 that I have now.

i'm using 40DCOE 136's... i've got the DCOE flange, CNC in aluminum... and it's not a big deal for me to finish cutting down a head side flange... i am having trouble finding the proper piping, though... i don't plan on supporting it with anything from the bottom, so it needs to be pretty hefty...

i think the cabs they are wanting to use are in the upper range of being good matches... some of the carbs that have been brought up are way too much for a 2 litre motor, unless they go with forced induction... that's why my choice is in the DCOE carb... tunability... too much fuel? whoopdee doo... change the jets, chokes, and/or venturies and you have a carb that behaves totally different...

that's my $.02

I bought a 4 to 2 barrel adapter b/c I couldnt find a 2 to 4 barrel adapter. I flipped it upside down and you can better visualize what I want to have my schools machine shop to make.

https://www.3geez.com/forum/attachmen...achmentid=3868
I plan to buy the carb I will use and then bring both the carb and intake manifold to the machine shop and see what they can do.


The only bad thing I see about doing the adapter plate from 2 to 4 barrel is the bolts that hold the adapter to the intake manifold would be exposed to the intake air and fuel. It might be easier to do that 2 barrel holley. I'm still not certain that those huge carbs will even be any good for our cars.

Here's a link I found about carb sizes. I must have been right when I remembered something in school about carbs are good if they're too big.

http://realbig.com/detomaso/1999-04/800.html


I think I did the math right I could have messed up who knows. But for our motors I think 462.9 cfm is optimal +/- 10% So it is possible for us to have a 500 cfm carb... What do you guys think about that?


edit: This looks like a pretty decent carb.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33550

And this one too.

http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WD1V

I think maybe our cars would rock if we added a little demon to them ;)
This guys has a ton of demon carbs and he live in my state. I'm going to try and call him and maybe he could help us out on what carb would be ideal for our applications. Here's a 500 cfm demon. And oh so pretty :)

http://cgi.ebay.com/ebaymotors/ws/eB...category=33550


Not too bad for $300


I would be a whole lot easier to adapt that 2 barrel 500 cfm road demon carb than a 4 barrel carb. 125 cfm per cylinder sounds pretty amazing to me. I have heard great things about demon carbs I just forgot about them until I ran across one on ebay. I could easily have an adapter plate made to fit out stock manifolds to these demon 2 barrel carbs. Demon has a 375cfm carb too. But I think the 500 cfm one would be nice and not too much overkill. I'm going to talk with the seller and see what he thinks about the cfm and maybe he can match something better who knows.... Basically I would just need to bring 2 gaskets to the machine shop at school and tell them how thick I want the plate and that I want to have that coolant passage blocked off on the intake manifold. Anyone that has a weber either knows that or found out the hard way ;) Yeah I was one of them... I shot coolant about 10 feet of the muffler. It was pretty funny seeing the green spray but man did that smell and freak us out.

So I want to know what you guys think about the 2 barrel 500 cfm demon? I think if we bored out our blocks and got some larger pistons we could get a bigger carb but with stock bottom ends and modfied top ends and other things 500cfm is plenty big.

-Mike

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That link isn't the best one for info... try "grapeape racing"
Our Engine CID is : 119
Our max rpm for now can be : 7,000
I would set your max rpm to where other parts on your motor like the header and cam can help out.
If you stick it at 8,000 and have a cam for 6,000 and have a header for 6,500 then you're selling yourself short.

VE is volumetric efficiency which is never at 100% in most N/A street cars but it is just used. Thats why most carb makers usually say go one carb size smaller then what you get when doing the calculations to account for loss of VE. You'll be much happier with a properly sized carb because it will be more responsive for the entire rpm range instead of having a bigger carb that is sluggish down low and only having some high rpm benifit. 104% was with ram air... usually only in forced induction motors does the VE go above 100%.


I put the A20's CFM up top already.

Quote:

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Originally Posted by A20A1

I was reading up some and found that I could increase the CFM the engine pulls by 52 if I divide the cylinders into pairs.
Below 3,600 rpm the divided plenum manifold makes more HP and Torque
Above 3,600 rpm the open plenum makes more HP and Torque

A20 @ 100% VE is good for 224 CFM @ 6,500 RPM
22R @ 100% VE is good for 270 CFM @ 6,500 RPM
*I used the 22R because there is a 500 CFM 4bbl conversion for it.)

Lets see if I'm doing this right
2bbl and 4bbl are rated differently for CFM

2bbl CFM = 4bbl CFM x 1.414
4bbl CFM = 2bbl CFM / 1.414

So the divided manifold would make the 4bbl into two 2bbl's
500 CFM 4bbl converted to 2bbl is 707 CFM but since it's split into two I divide by 2 right... so then I get 353.5 & 353.5 CFM carbs... which is just like having two 38 Webbers each feeding 2 cylinders.
390 CFM 4bbl converted to 2bbl is 551.46 CFM but since it's split into two I divide by 2 right... so then I get 275.73 & 275.73 CFM carbs which is just like having two 2bbl Keihins each feeding 2 cylinders.

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So basically it would better to get the smaller road demon carb 350 cfm. I'll have to check I can't remember what the weber 32/36 cfm is. Thanks for fixing up the info. I wasn't sure that info was 100% thanks for clearing it all up for us.

I can't remember what the cfm is of the 32/36 but I read online that the weber 38 has 370 cfm. So I think I'm going to find me a cheap 38 and rebuild it.

-Mike

Quote:

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Originally Posted by Mike's89AccordLX

Here's a link I found about carb sizes. I must have been right when I remembered something in school about carbs are good if they're too big.

http://realbig.com/detomaso/1999-04/800.html

I think I did the math right I could have messed up who knows. But for our motors I think 462.9 cfm is optimal +/- 10% So it is possible for us to have a 500 cfm carb... What do you guys think about that?
-Mike

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Mike, I think what the original person ment by 10% is -
090% to 100%
instead of
100% to 110%

CFM info I posted for the weber... I did some searching and found different CFM ratings for the same carbs... but they were all in about the same area... I then did an average CFM rating based on the info.

https://www.3geez.com/showthread.php?t=19464
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I honestly don't believe the 38 is more the 370 cfm... yet there was one place that rated it at 400 so I added that in.

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Quote:

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Originally Posted by Mike's89AccordLX

So basically it would better to get the smaller road demon carb 350 cfm. I'll have to check I can't remember what the weber 32/36 cfm is. Thanks for fixing up the info. I wasn't sure that info was 100% thanks for clearing it all up for us.

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I miss read his explination for 104%... I thought he said short ram... instead of ram air.
I was like WTF...
I edited my remark.
Anyways it still isn't the most informative site.

I just notticed something about the manifold adapter you posted... I made the same mistake the first time I installed mine... you actually need to turn the adapter 90 degrees.
If you install a 4bbl the way it is now then the secondaries will be closed to one half of the manifold and the primaries will be on the other. It wouldn't make too much of a difference if we had a big plenum and the carb sitting on a spacer, but that isn't the case.

Still it is a nice looking adapter. I'm sure it will be useful.
I would use some stainless bolts with a hex key insert head (like the ones for the weber adapter plate) instead of studs and nuts... and use a locking washer.
With a machine shop it should be easy to tap and drill new bolt holes... I think shepherd had to fill in areas with the alumaloy to get his adapter to work.

I'm just going to take the adapter back and get a weber 38. Seems that it would easier adaptable and useful for my car.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33550

Yeah the 38 will be easier to adapt... the 350 demon is a sweet carb though. And certainly more up to date the the 38. They are both around the same price.


Here are some fuel components if anyone was looking to run a bigger carb. http://www.edelbrock.com/automotive/fuelpumps.html

A little bigger is not going to hurt you. I know what those books say but thats really old tech. If your motor only takes 250 cfm then a 300 cfm carb isnt gonna cram any more air down it.Holley makes a 390 4 barrel carb its kinda pricey.

Demon makes a pretty good carb there have been some problems with them you need to look into that. There tech sucks. If you do get a Demon get the idle-eze carbs.. They had some major problems with getting the idle correct and came out with this new design. Thats why you see so many on E-bag every ones dumping the old design.

The VE on our cars could go over %100 in some areas RPM wise dont be surprised .Honda was no fool he new how to make power. There some scanvaging effects etc. that come into play.

wp

NEW PICS OF THE MANIFOLD PROGRESS UP SOON... gimmie a minuet

scroll to the top or go to the first page to see the updated pics.

so you are still keeping somewhat busy on the custom manifold? thats really interesting what your doing. guess you really need to know what your doing to attempt anything to this degree. guess you should be called the carb master of 3geez.

I think I said it best 2 years ago when I called him the Carb God of 3geez. I can only hope to know what he does about the carbs. I'm graduating in Auto mechanics this coming year and I still don't know as much as Mike about carbs. But that isn't too big on the list for mechanics to know nowadays :(

-Mike